ANGULAR-DISTRIBUTION OF DESORBING CARBON-DIOXIDE PRODUCED IN 2 PROCESSES ON A STEPPED PLATINUM(557) SURFACE

The oxidation process of adsorbed carbon monoxide ant the angular dist ribution of the desorbing product were studied on a stepped platinum ( 557) surface by means of isotope tracer and angle-resolved thermal des orption. Two CO2 formation processes are confirmed, i.e. the reaction of adsorbed CO with oxygen adatoms and with oxygen admolecules. The fo rmer process occurs in the temperature range 200-500 K, and the latter below 200 K. CO2 desorption in the Former process is collimated in th e direction close to the terrace normal, whereas the latter desorption is peaked at an angle of 7 degrees downwards from the bulk surface no rmal. CO2 formation takes place on different reaction sites. (C) 1997 Elsevier Science B.V.